Amalgam substitute

ABSTRACT

The invention relates to filling systems containing as component i) a sealing system which is capable of bonding to the tooth hard substance, as component ii) a filling material suitable for restorative dentistry, the filling system containing in addition a component iii) in component i) and/or component ii) which reduces the curing of the respective other component by disturbance of the curing mechanism only in the boundary layer between sealant and filling material such that the bonding between components i) and ii) is less than the bonding of component i) to the tooth hard substance.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/EP00/10342 which has an Internationalfiling date of Oct. 20, 2000, which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to a dental filling system for fillingtherapy and its use as amalgam substitute.

DISCUSSION OF CONVENTIONAL ART

Amalgams—for example a mixture of a silver-tin alloy with liquidmercury—have been used for 150 years as standard filling material inrestorative dentistry, being used in particular in the premolar andmolar tooth area. With correct use, amalgam restorations are capable ofguaranteeing the maintenance of tooth hard substance and also thevitality of the pulpa (so-called standard 1) and also the tooth form andfunction for years (so-called standard 2). Also decisive in thelong-term success of amalgam fillings was the simple processingtechnique and the relatively low cost, as the average survival rate ofan amalgam filling can be up to 10 years and more. Despite this, inrecent years amalgam has increasingly lost its share of the market asthe standard filling material. The main reason for this is thecontroversy about toxic and allergenic potential and also the damage tothe environment and the absence of tooth colour. As materials weresubsequently sought which could serve as substitute for amalgam, therewere two different options available: on the one hand, the amalgamalternatives were developed and on the other hand, amalgam substituteswere sought.

The aim of the amalgam alternatives is to design the restoration suchthat it is indistinguishable from the surrounding tooth and also remainsso during the whole application time (so-called standard 3).

As examples of this material group, there can be named in particularcomposites which are said to have not only the tooth colour but also acertain abrasion resistance and a perfect marginal adaptation. This isachieved by additionally using an adhesive system (also bond, bonding,bonding system, adhesive, sealant or sealing system) which must be usedaccurately in what is sometimes a complicated application.

In contrast to this, an amalgam substitute need only meet the previouslynamed standard 2; in addition, the practical application—according tothe amalgam—should take place simply and swiftly. This meant that itmust be possible for example to work with steel moulds and woodenwedges, that a simple filling technique can be used, and in particularif a light curing is envisaged, that the latter must be possibledirectly from the occlusal surface. The layer-by-layer construction ofthe filling required with amalgam alternatives should be dispensed withand instead—again according to the amalgam—a so-called bulk filling bepossible.

DE-A-196 03 577 describes an adhesive system which aims at amarginal-gap-free bond between the plastic material and tooth hardsubstance. The result of the excellent bond in such a system is that inthe case of a failure of the adhesive system, the fracture occursbetween tooth hard substance and the restorative material. This meanshowever that in the case of a fracture on or in the tooth hardsubstance, there is no longer any protection against caries.

DE-A-195 44 670 describes an adhesive system which does not cureradically but in which a condensation reaction product is formed. Inthis manner, an oxygen-inhibition layer is avoided. With the use of thisadhesive system—which again aims at the prevention of a marginalgap—according to the inventor, cohesive cracks in the dentine and enamelresult. Consequently, this system is not capable of reliably preservingthe tooth hard substance. The adhesive system therefore likewise belongsto a category which aims at an absolute bond between tooth hardsubstance and filling material without the cracking location being ableto be predicted should cracking take place. Consequently, it can alsooccur between bond and tooth hard substance.

EP-A-0 423 430 describes a dentine adhesive system with a primer and abond. Here also, a predominantly marginal-gap-free bond between toothhard substance and restorative material is aimed at without it beingable to be predicted where the marginal gap will occur in the case of afailure of the adhesive system.

EP-A-0 088 527 describes an enamel conditioner which is intended toproduce a better bond between enamel and filling material than resultsfrom the etching process by phosphoric acid normally used.

DE-A-34 14 163 describes a dentine primer and a dentine bonding systemwhich likewise aims at a predominantly marginal-gap-free bond betweentooth hard substance and filling material.

In the state of the art, these adhesive systems are not used as puresealing agent for the tooth hard substance. They are used exclusively asbonding material, the bond being produced between sealed tooth hardsubstance and the shrinking filling material. The adhesive systems ofthe state of the art uniformly aim at what is, in absolute terms, agreater bonding between the filling material and the tooth hardsubstance. The disadvantage of these systems is that it cannot bepredicted where, in the case of a failure of the adhesive system, acrack will occur. In particular fractures in the boundary layer betweenadhesive system and the tooth hard substance or in the tooth hardsubstance are very damaging. A reliable protection thus cannot currentlybe guaranteed with use of adhesive and filling systems of the state ofthe art.

Studies show that with the filling systems known from the state of theart, for example composites in combination with their adhesive systems,which were developed as amalgam substitute, fillings are producedwhich—in particular in the case of occlusal stress—lead in a very shorttime to a marginal gap of over 60%, sometimes even up to 95% and more.This leads to marginal discolorations—which would still be acceptablewithin the framework of standard 2—and the development of secondarycaries. With such marginal-gap phenomena, the risk of secondary cariesdevelopment must be regarded as high to very high.

The materials which are proposed as amalgam substitute in the state ofthe art thus do not meet the previously named standard 1, i.e. themaintenance of the tooth hard substance over a prolonged period of time.Such materials should be used at most as temporary fillings.

The reason for the failure of the known amalgam substitute materials isthat these materials normally display a volume shrinkage of 2.5 to 4.5%during curing. The resulting shrinkage stress on the bond and the toothhard substance exceeds the strength of the bond or even the tooth hardsubstance. Under this shrinkage stress, unpredictable fracturestherefore occur in the enamel or dentine or else also a break in thebond between tooth hard substance and adhesive system. Although anadhesive system is thus used, unprotected regions of the tooth hardsubstance result after the preparation, which are attributable to acohesive fracture or a break between bond and tooth hard substance.

WO-99/25309 describes metal-free dental filling systems as amalgamsubstitute which seeks to overcome the previously named disadvantages ofthe current state of the art. It describes a dental filling systemcontaining

-   a) a dental filling material and-   b) an adhesive or a sealant for tooth hard substance,-   c) the bond of the adhesive or the sealant to the tooth hard    substance being stronger than to the filling material such that no    destructive forces of the shrinking material are transmitted to the    adhesive or the sealant.

In technical terms, the following solutions are proposed concerningsame:

-   1. The use of an additional layer between filling material and    sealant which prevents the transmission of destructive forces onto    the sealant.-   2. Between adhesive and filling material, or between intermediate    layer and filling material, if present, there is no homo- or    copolymerization.    -   This can be realized for example:        -   through a low radical content, by applying a powder or a            coating, such as an organosilicone compound, which prevents            a wetting of the two boundary surfaces,        -   through a different polarity between filling material and            adhesive, which is likewise intended to prevent a wetting,        -   through a different hydrophobia or hydrophilia of filling            material and sealant,        -   through a different curing system of filling material and            sealant (for example a radically curing filling material and            a cationically curing sealant).

In particular with the last method, DE-A-199 37 092 shows that with useof different polymerizing systems a very good bonding between adhesiveand filling system is definitely achieved.

A major disadvantage of the technical solutions described is that newadhesive systems and/or filling systems which meet these requirementsmust be developed at high cost. None of the solutions shown in the nameddocument contains the simple addition of substances to the sealingand/or filling system which disturb the initiator system of therespective other component.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a simple dentalfilling system with which the bonding forces between sealant or adhesivesystem and filling material are weaker than between sealant or adhesivesystem and tooth hard substance, and which manages using customarydental materials and which requires no additional intermediate layer.Thus no new adhesive systems or filling materials need be developed.

This object is achieved by filling systems containing as component i) asealing system which is capable of bonding to the tooth hard substance,as component ii) a filling material suitable for restorative dentistry,the filling system containing in addition a component iii) in componenti) and/or component ii) which reduces the curing of the respective othercomponent by disturbance of the curing mechanism only in the boundarylayer between sealant and filling material such that the bonding betweencomponents i) and ii) is less than the bonding of component i) to thetooth hard substance.

The filling system according to the invention is thus such thatcomponent i) bonds to the tooth hard substance.

The terms “comprise” and “contain” indicate a non-conclusive enumerationof features.

The filling system preferably fulfils the equation a>0 and a>b>=0, aindicating the bonding value between tooth hard substance and sealingsystem and b the bonding value between sealing system and fillingmaterial.

The sealing system preferably bonds to the tooth hard substance suchthat after carrying out an adhesion test, more than 50%, preferably morethan 80% of the surface of the tooth hard substance in the regionexamined is coated with the sealing system.

Depending on the nature of component iii), this can be a quantity of0.01 to 99 wt.-%, preferably 0.25 to 95 wt.-% relative to the overallmass of component iii) and component in which component iii) iscontained. All wt.-% data given hereafter are based on this.

The invention also relates to a kit which comprises the filling systemaccording to the invention containing a sealing system and a fillingsystem. Sealing system and filling system are as a rule packedseparately from each other, preferably in the form of a disposable pack.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the invention is described in more detail.

The bonding between components i) and ii) can be completely removed. Itis clear for the dentist carrying out the treatment that he must thenundertake the preparation of the cavity—analogously to the methodcustomary with the amalgam—such that the retention of the fillingmaterial is mechanical (so-called undercut preparation).

Radical-forming initiators are described in detail in the literature(J.-P. Fouassier, Photoinitiation, Photopolymerization and Photocuring.Hanser Publishers, Munich, Vienna, N.Y., 1995). They can be substancesactivatable by UV- or visible light, such as benzoin alkyl ethers,benzil ketals, acylphosphinic oxides or aliphatic and aromatic1,2-diketone compounds, for example camphorquinone, the catalystactivity being able to be accelerated by the addition of activators,such as tertiary amines or organic phosphites, in a manner known per se.

If for example an acylphosphinic oxide is used as radical initiator inthe sealing system and a camphorquinone-amine system in the fillingmaterial, thus for example the catalyst of the filling material—i.e. theamine—can be inhibited by additions to the adhesive system—for exampleof acids. This takes place in such a way that, when the filling materialis brought into contact with the adhesive, the acid from the adhesivepenetrates the filling material, protonates the amine there and thusmakes the latter unusable as a radical acceptor. Consequently, noradical initiation can take place in the boundary layer and no bondingbetween filling material and adhesive is possible.

When using acids as component iii), those are preferred which have asufficient mobility of the protons, i.e. either a pKs value of <4.75 or,if their pKs value is greater than or equal to 4.75, are available insufficient quantity. This means for first acids, for example, the use ofstrongly inorganic acids such as mineral acids, e.g. hydrochloric acid,sulphuric acid, phosphoric acid, super acids such as HSbF₆ or HBF₄,Lewis acids such as e.g. BF₃ adducts, acid metal salts such as FeCl₃,AgNO₃, or complex acids or precursors of acids such as acid chlorides oranhydrides. Similarly, compounds can be used which form strong acidswith water or alcohols, such as saturated or unsaturated carboxylic acidhalides.

Also suitable are unsaturated phosphoric acid and phosphonic acidderivatives as described in DE-A-198 06 572.8 and EP-A-0 909 761.

Also preferred are the hydrolysis-stable polymerizable acrylphosphonicacids of DE-A-197 46 708.

Particularly preferred is the use of the above acids in the adhesivesystem, where in a more preferred version the filling system contains aninitiator system of camphorquinone and aliphatic amine.

It is true for second acids, such as more weakly acid acetic acid orcarbonic acid derivatives, that they must be made available within themeaning of the compositions according to the invention in such aquantity that a pH value of less than 6 results on the sealing layer.

If for example compounds are used in the adhesive system which arethemselves polymerizable and in addition are in a position to releaseprotons, these compounds correspond to component iii) and their contentcan lie between 0.1 to 99 wt.-%, preferably between 3 to 90 wt.-% andparticularly preferably between 5 to 75 wt.-%. The content of otheracids can—depending on acid strength—lie between 0.1 to 80 wt.-%,preferably between 3 to 70 wt.-% and particularly preferably between 5to 60 wt.-%.

Also suitable are acid fillers such as citric acid oracid-functionalized glasses or quartzes or those which make availablethe protons via other mechanisms, such as acid ion exchangers incombination with soluble salts. It is also conceivable to use these acidfillers likewise in the adhesive system, when their content should thenlie between 3 to 60 wt.-%, preferably between 5 to 53 wt.-% andparticularly preferably between 7 to 45 wt.-%. If they are used in thefilling material, the content lies between 30 to 85 wt.-%, preferablybetween 40 to 82 wt.-% and particularly preferably between 50 to 80wt.-%.

If the acids and/or acid fillers cannot be incorporated directly intothe matrix of the adhesive or the filling material, it is alsoconceivable to subsequently apply to the adhesive a dissolved orsuspended acid or an acid filler which then penetrates or diffuses intothe adhesive. Preferred solvents are those such as water, alcohols,ketones such as acetone, methyl ethyl ketone, or also short-chainedpolymerizable compounds such as 2-hydroxymethacrylate or(2,3-epoxypropyl)-methacrylate.

In principle, the acid strengths of the acids used can be increased byadditions of metal salts, the metal ions of which have a high affinityto the acid anion group.

A further possibility of the version according to the invention is forexample the addition of cations which are capable of forming strongcation-amine complexes, such as copper, zinc, cobalt, silver or ironions.

These compounds can be used in quantities of between 0.01 to 20 wt.-%,preferably between 1 to 10 wt.-% and particularly preferred between 1 to5 wt.-%.

Another possibility of the version according to the invention is forexample the addition of non-initiating amines—i.e. amines withoutabstractable α-protons such as triphenylamine or other HALS [hinderedamine light stabilizers] to—in this case—the adhesive. As here also, theamine in the boundary layer diffuses into the filling material, there ittakes over the place of the original initiator amine and thus preventsthe polymerization in the boundary layer, which results in a“non-bonding”. As examples of HALS there can be named triarylamines suchas triphenylamine, 1,2,2,6,6-pentamethyl piperidines or compounds suchas Tinuvin 292 or Tinuvin 123 (Ciba Speciality Chemicals, Switzerland).These amines can be used in quantities of between 0.01 to 22 wt.-%,preferably between 1 to 15 wt.-% and particularly preferably between 1to 12 wt.-%.

Similarly it is possible for example to inhibit the light-sensitivemolecule—i.e. for example camphorquinone—according to the same mechanismby additions in the boundary layer. For these additions, there can benamed for example:

-   -   Complexing agents for, for example, benzoin alkyl ethers, benzil        ketals, acylphosphinic oxides or aliphatic and aromatic        1,2-diketone compounds (for example camphorquinone) such as Li        salts or divalent chelating cations.    -   Compounds which react very fast with the previously named        molecules such as primary amines, thiols or hydrazines.

These compounds are used quantatively between 0.01 to 22 wt.-%,preferably between 1 to 15 wt.-% and particularly preferably between 1to 12 wt.-%.

Suitable initiator systems for triggering the radical polymerization viaa redox mechanism are also for example the peroxide/amine,peroxide/barbituric acid derivatives or peroxide/acids systems.

If such systems are present in one of the two components i) or ii), itis possible for example to use additions in the other component whichbind the amine irreversibly such as by acid chlorides or acidanhydrides. Naturally, the peroxide can also be inhibited in this way.

If one of the two components i) or ii) is cationically curing, additionswhich disturb the cationic initiation system are thus conceivable in theother component. Suitable as such additions are for example:

-   -   Basic compounds such as amines, basic salts, for example the        oxides or hydroxides of the elements of the first to third main        groups or sub-group, or basic fillers such as fine-grained        glasses, and alcoholate salts. Also suitable are alkaline and        alkaline earth halides and pseudohalides. Particularly preferred        are Li salts, in particular Li salts of strong acids such as Li        halides and Li tosylates.    -   With use of photoinitiator systems as described in DE-A-197 36        471 and in DE-A-197 43 564, additions for example such as the        acids, acylphosphinic oxides or non-initiating electron donors        described above are suitable.

These compounds can be used for example in quantities of between 0.01 to30 wt.-%, preferably between 1 to 25 wt.-% and particularly preferablybetween 1 to 20 wt.-%.

If these compounds cannot themselves be directly incorporated intocomponents i) or ii) due to for example solubilites or other effects, itis possible to dissolve or suspend them separately in a suitable solventand only then to apply them to one of the respective components, thedissolved or suspended compounds then penetrating or diffusing into therespective components.

The application of components i) and ii) takes place in customarymanner. In a preferred version, the tooth hard substance is not etchedbefore the application of component i). If component iii) displays acidproperties, a separate etching step is also not required, as the etchingprocess takes place during the application.

In a further preferred version of the invention, component ii) isapplied directly after component i).

EXAMPLES

In the following, the invention is described in more detail with thehelp of examples, which are to be considered as embodiments and in noway limiting.

Bonding Measurement on Bovine Teeth Through Adhesive Attachment of aFilling Material:

The adhesion bond was tested by an adhesion pull-off test on bovineteeth. Per test, 5 freshly extracted bovine teeth were ground down bymeans of sand paper until there was a sufficiently large exposed dentinesurface. Wax platelets with a punched-out hole measuring 6 mm were gluedonto each of these surfaces to obtain a standardized bonding surface. Aquantity of the test mixtures sufficient for complete wetting of thetest surface was then worked into the dentine surfaces with a microbrushfor 20 seconds, blown briefly with compressed air and polymerized bymeans of a light polymerization device (Elipar Highlight™, ESPE) for 20seconds. The filling material (Pertac II, ESPE, Seefeld) was thenintroduced into the holes of the wax platelets and fully polymerized by40 seconds' exposure to light. The wax platelet was removed and thetestpieces stored for 24 hours at 36° C. and 100% air humidity. Thetestpieces were then removed in a tensile test (Zwick Universal TestMachine).

The bonding values can be seen in Table 1.

To assess the residue of the sealant mixture, the sealant mixtures arereacted with 10 ppm Rhodamin B (Merck, Darmstadt) and the adhesion bondtested.

After carrying out the bonding test, a section 200 micrometers thickeach of filling material and tooth hard substance is preparedperpendicular to the tooth or filling surface. The sections of toothhard substance and filling material are observed by means of afluorescence microscope (for example Axioplan, Zeiss) and the residue ofthe sealant mixture measured.

Preparation of the Reference Mixture:

To prepare 10 g of the reference mixture, the following constituents areintensively mixed together:

-   -   3.000 g (30 wt.-%) 2-hydroxylethyl methacrylate;    -   6.900 g (69 wt.-%) 10-methacryloyloxylethyl phosphate;    -   0.100 g (1 wt.-%)        bis(2,6-dichlorobenzoyl)-(4-butylphenoxy)phosphinic oxide;        Preparation of Sealant Mixture 1 According to the Invention:

To prepare 10 g of the sealant mixture 1, the following constituents aremixed together intensively:

-   -   1.200 g (12 wt.-%) phosphoric acid;    -   3.000 g (30 wt.-%) 2-hydroxyethyl methacrylate;    -   5.700 g (57 wt.-%) 10-methacryloyloxyethyl phosphate;    -   0.100 g (1 wt.-%)        bis(2,6-dichlorobenzoyl)-(4-butylphenoxy)phosphinic oxide;        Preparation of the Sealant Mixture 2 According to the Invention:

To prepare 10 g of the sealant mixture 2, the following constituents aremixed together intensively:

-   -   1.600 g (16 wt.-%) citric acid;    -   2.600 g (26 wt.-%) 2-hydroxyethyl methacrylate;    -   5.700 g (57 wt.-%) 10-methacryloyloxyethyl phosphate;    -   0.100 g (1 wt.-%)        bis(2,6-dichlorobenzoyl)-(4-butylphenoxy)phosphinic oxide;        Preparation of the Sealant Mixture 3 According to the Invention:

To prepare 10 g of the sealant mixture 3, the following constituents aremixed together intensively:

-   -   0.800 g (8 wt.-%) triphenylamine;    -   2.600 g (34 wt.-%) 2-hydroxyethyl methacrylate;    -   5.700 g (57 wt.-%) 10-methacryloyloxyethyl phosphate;    -   0.100 g (1 wt.-%)        bis(2,6-dichlorobenzoyl)-(4-butylphenoxy)phosphinic oxide;        Preparation of the Sealant Mixture 4 According to the Invention:

To prepare 10 g of the sealant mixture 4, the following constituents aremixed together intensively:

-   -   0.600 g (6 wt.-%) aqueous LiCl solution (15.67 wt.-%)    -   3.000 g (30 wt.-%) 2-hydroxyethyl methacrylate;    -   6.300 g (63 wt.-%) 10-methacryloyloxyethyl phosphate;    -   0.100 g (1 wt.-%)        bis(2,6-dichlorobenzoyl)-(4-butylphenoxy)phosphinic oxide;

The sealant mixture 4 was used in the bonding measurement tests inconjunction with a cationically curing filling material instead ofPertac II.

The preparation of the cationically curing filling material is describedin the following:

In a three-finger kneader, the following constituents are kneaded into ahomogeneous paste. There are used for 100 g paste:

-   -   75.000 wt.-% (75.000 g) quartz (average grain size 0.9 μm, was        silanized with 5 wt.-% glycidyloxypropyltrimethoxysilane);    -   0.525 wt.-% (0.525 g)        4-methylphenyl-4-isopropylphenyl-iodoniumtetrakis-(penta-fluorophenyl)borate;    -   0.223 wt.-% (0.223 g) camphorquinone (Merck, Darmstadt);    -   0.001 wt.-% (0.001 g) ethyl-4-dimethylaminobenzoate (Merck,        Darmstadt);    -   0.001 wt.-% (0.001 g) 2-butoxyethyl-4-dimethylaminobenzoate;    -   12.125 wt.-% (12.125 g) 3,4-epoxycyclohexyl-3,4-epoxycyclohexane        carboxylate;    -   12.125 wt.-% (12.125 g)        1,3,5,7-tetrakis-(2,1-ethanediyl-3,4-epoxycyclohexyl)-1,3,5,7-tetramethylcyclotetrasiloxane.        Preparation of the Sealant Mixture 5 According to the Invention:

The following constituents are mixed together corresponding to sealantmixtures 1 to 4 and both the bonding and the residue of the sealantlayer examined:

-   -   methacrylated phosphoric acid esters;    -   water    -   hydroxyethylene methacrylate;    -   bis-GMA;    -   acylphosphinic oxide;

The bonding was 3.5 MPa on dentine; the sealant layer remainedpredominantly on the tooth hard substance.

TABLE 1 Bonding of the sealant mixtures described in the examples:Sealant mixture Filling material Bonding [MPa]* Reference mixture PertacII (ESPE Dental 2.3 AG, Seefeld) Sealant mixture 1 Pertac II (ESPEDental 0.0 AG, Seefeld) Sealant mixture 2 Pertac II (ESPE Dental 0.0 AG,Seefeld) Sealant mixture 3 Pertac II (ESPE Dental 0.0 AG, Seefeld)Sealant mixture 4 Cationically curing 0.0 Sealant mixture 5 Pertac II(ESPE Dental 3.5 AG, Seefeld) *Average value of 5 measurements

With the sealant mixtures 1 to 4, no bonding of the filling material tothe bond took place. The bond remained largely undamaged on the toothhard substance after removal of the filling material. With the referencemixture on the other hand, the sealant mixture remained predominantly onthe filling material.

As the sealant mixtures according to the invention remain predominantlyon the tooth hard substance, it is proved that the bonding of thesealant mixture to the tooth hard substance is greater than to therespective filling material.

1. A filling system comprising: (i) a curable sealant component which iscapable of bonding to a tooth hard substance, (ii) a curable fillingmaterial component suitable for restorative dentistry, and (iii) acuring reduction component selected from the group consisting of: acidshaving a pKa value of less than 4.75, Lewis acids, acid metal salts,acid precursors, compounds which form strong acids with water, compoundswhich form strong acids with alcohols; a cation which forms cation-aminecomplexes; a non-initiating amine; a lithium salt; a divalent chelatingcation compound; oxides of elements of the first to third main groupsand subgroups of the Periodic Table of Elements, hydroxides of elementsof the first to third main groups and subgroups of the Periodic Table ofElements, alkaline halides, alkaline earth halides and pseudohalides;wherein said component (iii) is incorporated in the said component (i)and component (ii), and wherein, upon curing of the sealant and fillingmaterial components, component (iii) reduces curing only in a boundarylayer between sealant component and filling material component such thatthe bonding between the cured sealant component and the cured fillingmaterial component is less than the bonding of the cured sealantcomponent to the tooth hard substance.
 2. The filling system accordingto claim 1, wherein one of the sealant component (i) or the fillingmaterial component (ii) comprises as a curing initiation system acamphorquinone-amine system, and the other of these components comprisesas a curing initiation system an acylphosphine system.
 3. The fillingsystem according to claim 1, wherein the filling material component (ii)is cationic, and the curing reduction component (iii) is incorporated inthe sealant component (i) which cures radically.
 4. The filling systemaccording to claim 1, wherein the curing reduction component (iii) is anacid having a pKa value of less than 4.75 selected from the groupconsisting of hydrochloric acid, sulphuric acid, phosphoric acid, HSbF₆,HBF₄, BF₃ adducts, FeCl₃, and AgNO_(3.)
 5. A filling system according toclaim 1, wherein the curing reduction component (iii) is with a cationselected from the group consisting of copper, zinc, cobalt, silver andiron cations.
 6. A filling system according to claim 1, wherein thecuring reduction component (iii) is a non-initiating amine selected fromthe group consisting of triphenylamine and hindered amine lightstabilizers.
 7. A filling system according to claim 1, wherein thecuring reduction component (iii) is a non-initiating amine selected fromthe group consisting of triphenylamine and 1,2,2,6,6-pentamethylpiperidines.
 8. A filling system according to claim 1, wherein thecuring reduction component (iii) is a lithium salt selected from thegroup consisting of lithium halides and lithium tosylates.
 9. A kitcomprising a filling system comprising (i) a curable sealant which iscapable of bonding to the tooth hard substance, (ii) a curable fillingmaterial suitable for restorative dentistry, and (iii) a curingreduction component selected from the group consisting of: acids havinga pKa value of less than 4.75, Lewis acids, acid metal salts, acidprecursors, compounds which form strong acids with water, compoundswhich form strong acids with alcohols; a cation which forms cation-aminecomplexes; a non-initiating amine; a lithium salt; a divalent chelatingcation compound; oxides of elements of the first to third main groupsand subgroups of the Periodic Table of Elements, hydroxides of elementsof the first to third main groups and subgroups of the Periodic Table ofElements, alkaline halides, alkaline earth halides and pseudohalides;wherein said curing reduction component (iii) is incorporated in thesealant and/or the filling material, and reduces curing only in aboundary layer between the sealant and the filling material such thatthe bonding between the cured sealant and the cured filling material isless than the bonding of the cured sealant to the tooth hard substance,wherein the sealant and the filling material are packed separately fromeach other.
 10. The kit according to claim 9, wherein the curingreduction component (iii) is packed separately from the sealantcomponent (i) and the filling material component (ii).
 11. A method forfilling a tooth, comprising the steps of: (a) applying a sealant to thetooth hard substance, (b) optionally exposing the sealant to light, (c)applying a filling material, (d) exposing the filling material to light,and (e) applying to the sealant before step (c), or incorporating intothe sealant or filling material before application thereof, a curingreduction component selected from the group consisting of: acids havinga pKa value of less than 4.75, Lewis acids, acid metal salts, acidprecursors, compounds which form strong acids with water, compoundswhich form strong acids with alcohols; a cation which forms cation-aminecomplexes; a non-initiating amine; a lithium salt; a divalent chelatingcation compound; oxides of elements of the first to third main groupsand subgroups of the Periodic Table of Elements, hydroxides of elementsof the first to third main groups and subgroups of the Periodic Table ofElements, alkaline halides, alkaline earth halides and pseudohalides;wherein said curing reduction component reduces curing in a boundarylayer between the sealant and the filling material, such that bondingbetween the cured sealant and the cured filling material is less thanbetween the cured sealant and tooth hard substance when neither thesealant nor the filling material contains said curing reductioncomponent.
 12. The method according to claim 11, wherein the tooth hardsubstance is not etched before step (a).
 13. The method according toclaim 11, wherein the filling material is applied directly after theapplication of the sealant.